Aging treatment for Ni-Cr-Mo alloys

ABSTRACT

A single step heat treatment for Ni-Cr-Mo alloys containing from 12% to 19% chromium and from 18% to 23% molybdenum provides higher yield strength, high tensile strength and other mechanical properties comparable to those observed in similar alloys age-hardened according to current practices. This treatment is done over a total time of at least 4 hours and preferably less than 50 hours. However, the treatment works for only those alloys having alloying elements present in amounts according to an equation here disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This is a continuation-in-part application of U.S. patentapplication Ser. No. 09/894,353, filed Jun. 28, 2001, now pending.

FIELD OF THE INVENTION

[0002] The invention relates to heat treatment processes fornickel-chromium molybdenum-alloys having a chromium content of from 12to 19 weight percent.

BACKGROUND OF THE INVENTION

[0003] It is well-known that chromium imparts corrosion resistance tonickel base alloys. Therefore, Ni-Cr-Mo alloys and particularly thosewith chromium content of 15 to 24% have been popular for use incorrosive environments such as encountered in the chemical andpetrochemical industries.

[0004] Age-hardening is a process used in the metallurgical industry togive an alloy composition higher strength, as measured by its yieldstrength, tensile strength, and by notched stress rupture teststypically used in the art. Various applications demand a combination ofhigh tensile strength and low thermal expansion properties. One suchapplication is in the aerospace industry. Another application is sealrings used in land-based gas turbines. A combination of high tensilestrength and ductility is also very useful for bolts. Because of thedemanding operating conditions and performance parameters for metalproducts in these applications, various methods of age-hardening havebeen used. One common technique is to heat the alloy to a selected hightemperature, hold the alloy at that temperature for a period of time andthen cool the alloy to room temperature. For some alloy compositions,the alloy may be heated to one temperature, cooled, heated again to asecond temperature and cooled. Examples of these processes are disclosedin U.S. Pat. No. 3,871,928. The temperatures and time periods used toage harden an alloy depend upon the composition of the alloy. For allage-hardenable commercial alloys there are established times andtemperatures used that have become standard in the industry because theyare known to produce the desired properties. For Ni-Cr-Mo alloys havinghigh chromium content, that is chromium greater than 12% , the generalview in the art is that heat treatment beyond the initial annealing inan effort to improve mechanical properties would be impractical due tothe lengthy required times (hundreds to thousands of hours) and suchtreatments simply have not been done.

[0005] Solid-solution strengthened nickel- chromium-molybdenum(Ni-Cr-Mo) alloys and nickel-molybdenum (Ni-Mo) alloys are widelyutilized for commercial applications in the chemical industry, forexample. Generally, considered to be single phase materials, discountingthe presence of minor carbide phases, alloys such as these are notusually considered responsive to heat treatment, and are therefore usedin the annealed condition. There are exceptions, where some particularalloys do exhibit a commercially exploitable age hardening response.However, in these instances the age-hardening response observed isattributable to other elements, such as niobium, aluminum and titaniumbeing present in the alloy composition. The exception to this isHAYNES®242™ alloy which will be discussed later. The fact that Ni-Cr-Moand Ni-Mo alloys are not commercially age-hardenable does not mean thatthey do not exhibit any metallurgical response to thermal exposure atintermediate temperatures. Actually, alloys of this type can exhibitcomplex secondary phase reactions when exposed in the temperature rangefrom about 1000° F. to 1600° F. Unfortunately, the phases which form canoften be deleterious to both alloy ductility and other aspects ofservice performance. This is particularly observed with Ni-Mo alloyscontaining about 25 to 30% molybdenum. In such materials, exposure attemperatures from about 1000° F. to 1600° F. can result in the rapidformation of embrittling Ni₃Mo or Ni₄Mo phases in the microstructure.This can be a problem for both component manufacturing and for componentperformance.

[0006] For lower molybdenum, higher chromium, content Ni-Cr-Mo alloyswith about 16% molybdenum and 16% chromium weight percent content, theoccurrence of these particular intermetallic phases is not usuallyobserved after short term thermal exposures. With longer term exposureat temperatures from about 1000° F. to 1200° F., there is a distinctlydifferent metallurgical response. After about 500 to 1000 hours thepresence of the phase Ni₂(Mo,Cr) is evidenced in the microstructure. Along-range-ordered phase, with structure similar to that of Pt₂Mo , theNi₂(Mo,Cr) phase serves to significantly increase the strength of thesematerials without a severe loss of ductility. The one major drawback isthe prolonged aging time required to produce this phase.

[0007] There are several United States patents that disclose Ni-Cr-Moalloys. U.S. Pat. No. 4,818,486 discloses a low thermal expansion nickelbased alloy that contains 5% to 12% chromium and 10% to 30% molybdenum.The patent teaches that the aging times typically required to obtaindesired hardness without deleterious phases being formed is well over1000 hours at temperatures of 1200° F. to 1500° F. for most Ni-Mo-Cralloys. However, the aging time to harden the alloy compositiondisclosed in the '486 patent is as little as 24 hours at 1200° F. Thealloy of this patent has been marketed under the trademarks 242 alloyand HAYNES 242 alloy. HAYNES 242 alloy has been sold for applicationsrequiring high tensile strength and a low coefficient of thermalexpansion. Other beneficial properties of the 242 alloy include goodthermal stability, good low cycle fatigue resistance, and excellentcontainment capabilities due to its tensile strength and ductility.HAYNES 242 alloy consists of about 8% (weight percent) chromium, about20-30% molybdenum, about 0.35% to up to about 0.5% aluminum, up to 0.03%carbon, up to about 0.8% manganese, up to about 0.8% silicon, up toabout 2% iron, up to about 1% cobalt, up to about 0.006% boron, and thebalance weight percent being nickel.

[0008] There is a need for a shorter commercially exploitable agehardening process for Ni-Mo-Cr alloys with higher Cr levels (>12% Cr)than found in U.S. Pat. No. 4,818,486 that avoids formation ofdeleterious Ni₃Mo and Ni₄Mo phase, as well as mu-phase occurrence.

[0009] Another Ni-Cr-Mo alloy is disclosed in U.S. Pat. No. 5,019,184 toCrum et al. That alloy contains 19% to 23% chromium and 14 to 17.5%molybdenum. The patent discloses homogenization heat treatment attemperatures ranging from 1149° C. to 1260° C. for periods of from 5 to50 hours. The purpose of the treatment is to produce a corrosionresistant alloy having a desired microstructure rather than tostrengthen the alloy. No tensile strength data is given for any of thesesamples disclosed in the patent. The alloy of this patent has beencommercialized under the designation INCONEL® alloy 686.

[0010] Yet another corrosion resistant Ni-Cr-Mo alloy is disclosed inU.S. Pat. No. 4,906,437 to Heubner et al. This alloy contains 22% to 24%chromium and 15% to 16.5% molybdenum. There is no disclosure of any heattreatment or age hardening of this alloy. The alloy disclosed in thispatent has been commercialized under the designation VDM NICROFER 923 hMo or Alloy 59.

[0011] A high yield strength Ni-Cr-Mo alloy is disclosed in U.S. Pat.No. 4,129,464 to Matthews et al. This alloy contains 13% to 18% chromiumand 13% to 18% molybdenum. The patent says that the alloy could be agedusing a single step aging treatment of at least 50 hours at 900° F. to1100° F., but all examples are aged 168 hours or more. The statementthat at least 50 hours is required was an extrapolation of the resultsobtained from a 168 hours aging treatment. The patent reports data forthree alloys numbered 1, 2 and 3. Alloy 1 is commercially availableunder the trademark HASTELLOY® C-276 alloy. Alloy 2 is commerciallyavailable as HASTELLOY C-4 alloy. Alloy 3 is commercially available asHASTELLOY S alloy.

SUMMARY OF THE INVENTION

[0012] We provide a single-step age hardening process for certainnickel-chromium-molybdenum alloys containing from 12% to 19% chromiumand from 18% to 23 % molybdenum that results in higher yield strength,high tensile strength and comparable other mechanical properties asthose observed with the current age-hardening process used in the art,such properties being measured by yield strength, tensile strength, andtensile ductility tests at room temperature. This process works only forthose alloys in which the other alloying elements are present in amountsso that the composition has a P value that is within the range of 31.2to 35.9 where P is defined by the equation:

P=2.46Al+0.19Co+0.83Cr−0.16Cu+0.39Fe+0.59Mn+1.0Mo+0.81Zr+2.15Si+1.06V+0.39W+0.68Nb +0.52Hf+0.45Ta+1.35Ti

[0013] The alloys are aged at about 1100° F. to 1325° F. for at least 4and preferably 48 hours and then air cooled. When so treated the alloyswill have tensile properties suitable for use in applications requiringhigh tensile strength and ductility. By using this relatively shortsingle step aging process high chromium content nickel based alloyshaving a combination of high yield strength and ductility properties canbe made at lower cost than other alloys having such properties.Consequently, the present alloy is a more affordable alloy forapplications requiring such properties.

DESCRIPTION OF THE FIGURES

[0014]FIG. 1 is a graph of the alloys tested based upon the P value andchromium content of the alloy.

[0015]FIG. 2 is a graph of the alloys tested based upon the P value andmolybdenum content of the alloy.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] We provide a single-step aging treatment for Ni-Cr-Mo alloyscontaining from 12% to 19% chromium to produce an alloy for applicationsrequiring corrosion resistance, high tensile strength and excellenttensile ductility. This process involves age hardening the alloy atabout 1100° F. to about 1325° F. for at least 4 hours and then coolingthe alloy to room temperature. We have found, however, that this processprovides acceptable mechanical properties for only those alloys thatcontain alloying elements in amounts that provides a P value of from31.2 to 35.9, P being defined as:

P=2.46Al+0.19Co+0.83Cr−0.16Cu+0.39Fe+0.59Mn+1.0Mo+0.81Zr+2.15Si+1.06V+0.39W+0.68Nb +0.52Hf+0.45Ta+1.35Ti

[0017] We tested 13 nickel base test alloys and 3 Ni-Cr-Mo commercialalloys whose compositions are set forth in Table 1. The commercialalloys were HASTELLOY S sheet, HASTELLOY C-276 sheet, and HASTELLOY C-4sheet and plate. The thickness of each sheet was 0.125 inches and theplate was 0.375 inches thick. The designation “n.m.” in Table 1indicates that the presence of an element was not measured. Table 1 alsoreports the P value for each alloy.

[0018] The chromium content of the test alloys ranged from 11.56% foralloy 6 to 22.28% for alloy 10. Molybdenum ranged from 14.73% in alloy10 to 23.89% in alloy 13. All of the alloys contained similar amounts ofaluminum, cobalt, iron, and manganese. Tungsten was present within arange of 0.13 to 0.34. The alloys also contained small amounts of boron,carbon, cerium, copper, magnesium, phosphorus, sulfur, silicon, andvanadium. The test alloys were annealed after hot rolling to 0.5″ plateat annealing temperatures in the range of 1900° F. to 2000° F. forthirty minutes and water quenched. The commercial alloys were cut fromsheets or plate available from the manufacturer. All of the test alloyswere treated with a single-step aging treatment in which they were agedat 1200° F. for 48 hours. Then they were air cooled to room temperature.The commercial alloys HASTELLOY S, HASTELLOY C-276 and HASTELLOY C-4alloys, were aged at 1100° F. for 50 hours. Then they were air cooled toroom temperature. This 50 hour treatment corresponds to the treatmentproposed for those alloys by Matthews et al. in U.S. Pat. No. 4,129,464.TABLE 1 Composition of Samples Tested Composition Alloy Al B C Ce Co CrCu Fe Mg Mn  1 0.15 0.002 0.003 0.008 0.05 12.79 0.04 1.11 <0.002 0.33 2 0.15 0.002 0.002 0.007 0.04 15.26 0.01 1.13 <0.002 0.34  3 0.12 0.0030.006 0.008 0.05 14.99 0.03 1.05 <0.002 0.32  4 0.12 0.005 0.002 <0.0050.08 17.36 0.03 1.08 0.003 0.32  5 0.17 0.003 0.002 <0.005 0.06 19.880.02 1.05 <0.002 0.32  6 0.15 <0.002 0.003 0.007 0.05 11.56 0.06 1.170.003 0.34  7 0.14 0.002 0.004 0.005 0.06 16.57 0.04 1.08 0.004 0.31  80.16 0.002 0.004 0.009 0.06 12.58 0.04 1.17 0.003 0.30  9 0.13 0.0020.003 0.004 0.06 17.53 0.04 1.11 0.002 0.31 10 0.17 0.002 0.006 0.0050.06 22.28 0.01 1.17 0.002 0.30 11 0.14 <0.002 0.007 0.004 0.05 19.920.01 0.98 <0.002 0.29 12 0.13 <0.002 0.007 0.005 0.06 17.92 0.01 1.040.002 0.27 13 0.14 <0.002 0.006 0.006 0.06 13.45 <0.01 1.00 0.002 0.27Hastelloy 0.21 0.010 0.010 Ti < 0.01 0.05 14.92 <0.01 0.42 0.01 0.55 SC-276 0.23 <0.002 0.003 Ti < 0.01 1.53 15.55 0.07 5.99 0.02 0.50 C-40.34 <0.002 0.002 Ti 0.23 <0.1 15.54 0.02 1.01 0.05 0.18 plate C-4 0.34<0.002 0.003 Ti 0.21 <0.1 15.57 0.03 0.84 0.02 0.18 sheet Composition PAlloy Mo Nb Ni (Phos) S Si V W “P value”  1 21.58 n.m. 63.68 <0.0040.001 <0.01 0.01 0.19 33.3  2 19.92 n.m. 62.83 <0.004 0.002 <0.01 0.020.34 33.8  3 18.78 n.m. 64.55 0.002 0.001 0.01 <0.01 0.15 32.2  4 17.21n.m. 63.44 0.003 0.001 0.02 <0.01 0.14 32.7  5 15.40 n.m. 63.23 0.0050.001 0.03 <0.01 0.14 33.1  6 19.75 n.m. 66.37 <0.004 0.001 0.15 0.020.15 30.8  7 15.60 n.m. 65.99 <0.002 0.003 0.07 0.02 0.15 30.6  8 22.48n.m. 62.46 <0.004 <0.001 0.15 0.02 0.22 34.4  9 18.63 n.m. 61.84 <0.0040.003 0.11 0.02 0.15 34.5 10 14.73 n.m. 61.22 0.005 0.001 0.16 0.02 0.1634.7 11 17.36 0.03 60.98 <0.002 0.001 0.05 0.03 0.13 35.1 12 20.08 0.0360.24 0.005 0.001 0.04 0.03 0.14 36.1 13 23.89 0.03 61.41 0.002 0.0010.04 0.03 0.15 36.2 Hastelloy 14.48 n.m. Bal. 0.011 <0.002 0.36 n.m.<0.1 28.7 S C-276 15.41 <0.05 Bal. 0.007 0.001 0.04 0.15 3.98 33.6 C-415.41 <0.05 Bal. <0.005 <0.002 0.04 0.02 <0.1 30.1 plate C-4 15.24 n.m.Bal. 0.013 <0.002 0.04 0.02 <0.1 29.9 sheet

[0019] All of the samples were tested to determine their tensileproperties. The tests determined yield strength, ultimate tensilestrength, and percent elongation by following the standard ASTM E-8 testprocedures for such alloys. The results of those tests are reported inTable 2 TABLE 2 Room Temperature Tensile Properties for Sample Alloys(Aged 1200° F./48 hr/AC) Ultimate 0.2% Yield Tensile Strength StrengthPercent Alloy (ksi) (ksi) Elongation 1 114.2 185.9 41.0 2 116.3 187.540.5 3 107.9 179.3 43.0 4 51.2 115.7 63.7 5 56.6 117.0 59.9 6 50.3 120.463.8 7 46.9 113.3 63.7 8 112.6 183.7 43.6 9 79.5 153.0 50.8 10 50.1113.7 61.7 11 51.2 116.7 63.2 12 125.5 192.7 32.6 13 129.3 205.5 30.0

[0020] To be acceptable an alloy must have elongation values greaterthan 40 percent and yield strengths greater than 73 ksi. Alloys 1, 2, 3,8 and 9 all had acceptable properties. Alloys 12 and 13 did not possessenough tensile ductility as measured by the percent elogation. Alloys 4,5, 6, 7, 10 and 11 did not possess a high enough yield strength. Sincethe chromium content and molybdenum content of alloy 12 is within therange of chromium content and molybdenum content of the acceptablealloys it is clear that neither chromiumm content nor molybdenum contentis the sole predictor of acceptable tensil properties in this class ofalloys. We concluded that it is the interaction of nearly all of thealloying elements that is the predictor of such properties. Indeed, wediscovered that when the alloy has a P value in the range of 31.2 to35.9, chromium in the range of 12% to 19% and molybdenum in the range of18% to 23% were acceptable tensile properties achieved with this agingprocess.

[0021]FIG. 1 is a graph of the tested alloys based upon the P value ofthe alloy and the chromium content. Each alloy that had acceptabletensile properties is plotted with a dot. An X is used to plot thosealloys whose tensile properties were not acceptable after the alloy wassubjected to the two-step aging treatment. A box has been drawn aroundthe acceptable alloys. It is readily apparent from FIG. 1 that theacceptable alloys have a chromium content of 12% to 19% and a P valuewithin the range of 31.2 to 35.9.

[0022]FIG. 2 is a graph similar to FIG. 1 but plots the P value of thealloy against the molybdenum content. As shown in FIG. 2, the acceptablealloys contain from 18% to 23% molybdenum. The fact that Alloy 4 did notpass the tensile property requirements even though its chromium contentis within the desired range indicates that molybdenum content is alsocritical. Alloy 4 had only 17% molybdenum.

[0023] Having identified the compositions of alloys that could besuccessfully age-hardened 1200° F. to 48 hours and air cooled we thenlooked to see if the alloys disclosed by Matthews et al. in U.S. Pat.No. 4,192,464 would have acceptable properties when treated at 1100° F.for 50 hours. That patent at column 4, lines 4-5 contains a statementthat the data obtained and there reported for longer treatments suggeststhat aging for about 50 hours at 1100° F. will be effective. Testsamples were cut from commercially available HASTELLOY S sheet,HASTELLOY C-276 sheet and HASTELLOY C-4 sheet and HASTELLOY C-4 plate.The thickness of the sheets was 0.125 inches and the plate was 0.375inches thick. The composition of these alloys is in Table 1. Thesesamples were aged at 1100° F. for 50 hours and then air cooled. The agedsamples were then tested to determine their tensile strength propertiesusing standard ASTM E8 test procedures. The results of those tensiletests are reported in Table 3. TABLE 3 Room Temperature TensileProperties for Commercial Alloys (Aged 1100° F./50 hr/AC) Ultimate 0.2%Yield Tensile Strength Strength Percent Alloy (ksi) (ksi) ElongationHastelloy S 66.0 133.8 46.8 C-276 68.5 124.5 55.2 C-4 plate 58.1 125.555.2 C-4 sheet 94.5 153.4 43.9

[0024] All of the samples had acceptable tensile strength andelongation. The yield strength of HASTELLOY S sheet, C-276 sheet and C-4plate samples were below 73 ksi and consequently were unacceptable. TheC-4 sheet had acceptable yield strength and unlike the C-4 plate wasacceptable. The difference in yield strength between the C-4 sheet andthe C-4 plate is likely attributable to some unknown phenomenon,possibly a surface phenomenon, that gives thin specimens higher yieldstrength than thicker samples. Whatever the reason for the difference,the test data indicates that, contrary to Matthews' suggestion, a 50hour aging treatment at 1100° F. will not produce acceptable results forall Ni-Cr-Mo alloys. Indeed, it only worked for a thin sample of asingle alloy. The present process works for all forms of alloys meetingthe chromium, molybdenum and P value specified here. All of the threecommercial alloys had less than 18% molybdenum. Furthermore, C-4 alloyand HASTELLOY S alloy had P values below 31.2. As our data demonstratesa single step aging treatment as short as 48 hours provides acceptabletensile properties for all forms of only those Ni-Cr-Mo alloys having12% to 19% chromium, 18% to 23% molybdenum and a P value of from 31.2 to35.9.

[0025] Those skilled in the art will recognize that while chromium andmolybdenum must be present with the ranges encompassed by the testspecimens, other alloying elements are not co limited. Indeed, thoseelements could be present in amounts within the ranges set for in theUNS descriptions for commercially available Ni-Cr-Mo alloys whichinclude those tested here and alloys such as C-2000® alloy, C-22® alloy,SM 2060 Mo alloy and MAT-21 alloy. More specifically there could be upto 0.5% aluminum, 0.015% boron, 0.02% carbon, 2.5% cobalt, 2.0% copper,3.0% iron, 1.5% manganese, 1.25% niobium, 0.04% phosphorus, 0.03 %sulfur, 0.75% silicon, 2.2% tantalum, 0.7titanium, 0.35% vanadium and4.5% tungsten and 0.1% of a rare earth element.

[0026] Having now defined the alloys that can benefit from this agehardening process we considered what time and temperature range would beacceptable. A series of aging treatments was given to Alloy 2 and Alloy8. After the aging treatments were performed the hardness was measuredto determine whether the samples had age hardened. The results are shownin Tables 4 and 5. TABLE 4 The Effect of Different Aging Treatments onthe Hardness of Alloy 2 Temp (° F.) Time (h) Hardness (Rc) Unaged —<20.0 1100 48 20.6 1200 24 31.3 1200 48 36.1 1250 48 <20.0 1300 48 <20.0

[0027] TABLE 5 The Effect of Different Aging Treatments on the Hardnessof Alloy 8 Temp (° F.) Time (h) Hardness (Rc) Unaged — <20 1100 48 20.11200 48 34.3 1250 2 <20 1250 4 27.1 1250 8 39.9 1250 12 34.6 1250 1635.0 1250 48 35.8 1300 8 <20 1300 12 <20 1300 16 33.1 1300 48 35.3 132548 28.6 1350 48 <20 1400 48 <20

[0028] A sample was determined to have age hardened if it had a RockwellC (Rc) hardness value of more than 20.0. A sample in the unagedcondition confirmed that the material started out with a hardness ofless than 20.0. All samples given aging treatments at 1200° F. for about24 to 48 hours were found to strongly age harden. The samples aged at1100° F. for 48 hours just barely hardened. The samples of Alloy 2 agedat 1250° F. and 1300° F. for 48 hours did not harden. However, samplesof Alloy 8 did age harden when treated at 1250° F. and 1300° F. for 48hours. Indeed, Alloy 8 age hardened when treated at 1250° F. for timesranging from 4 hours to 48 hours. At 1300° F. age hardening did notoccur in Alloy 8 at 8 or 12 hours, but did occur when the treatment timewas 16 and 48 hours. Furthermore, Alloy 8 age hardened when treated at1325° F. for 48 hours. The difference between the responses of Alloys 2and 8 to heat treatment times and temperatures can be attributed to thefact that Alloy 8 has higher molybdenum and lower chromium than Alloy 2.The test results indicate that the alloy should be age hardened for atleast about 4 hours at a temperature ranging from about 1100° F. toabout 1325° F. Even though the longest aging time used in our tests was48 hours longer aging times could be used. However, we prefer that theage-hardening treatment here disclosed be done in a total time of lessthan 100 hours and preferably less than 50 hours. Indeed we prefer tocomplete the process in 48 hours. By using heat treatments totaling lessthan 100 hours, and preferably not greater than 50 hours, one canproduce lower cost, high chromium, Ni-Cr-Mo alloys that have desirabletensile properties. While the process here disclosed may also work whentotal aging times exceed 100 hours, the energy costs associated withsuch treatments make the process less desirable and commerciallyimpractical.

[0029] This process represents a significant advancement. Prior to thepresent invention Ni-Cr-Mo alloys having greater that 12% chromium werenot produced in the age hardened condition since the required agingtimes were considered to be too great. Because of the energy costsassociated with such long treatments the estimated cost of a higherchromium, age-hardened alloy was considered too high and no such alloysare in commercial existence. The single-step age-hardening treatmenthere disclosed will produce lower cost, high chromium, Ni-Cr-Mo alloysthat have desirable tensile properties.

[0030] Although we have described certain present preferred embodimentsof our alloy and method of producing that alloy, it should be distinctlyunderstood that our invention is not limited thereto but may bevariously embodied within the scope of the following claims.

We claim:
 1. A nickel-chromium-molybdenum alloy comprised of: from 12%to 19% chromium; from 18% to 23% molybdenum; up to about 0.5% aluminum;up to 0.02% carbon; up to about 1.5% manganese; up to about 3.0% iron;up to about 2.5% cobalt; up to about 4.5% tungsten; up to about 0.015%boron; and a balance of nickel plus impurities; wherein the alloy has aP value of from 31.2 to 35.9, P being defined as:P=2.46Al+0.19Co+0.83Cr−0.16Cu+0.39Fe+0.59Mn+1.0Mo+0.81Zr+2.15Si+1.06V+0.39W+0.68Nb +0.52Hf+0.45Ta+1.35Ti and thealloy is age hardened at about 1100° F. to about 1325° F. for at least 4hours then cooled to room temperature.
 2. The alloy of claim 1 whereinthe alloy is age hardened in not more than 50 hours.
 3. The alloy ofclaim 1 wherein the alloy is age hardened at about 1200° F. for 48hours.
 4. The alloy of claim 1 also comprising: up to about 0.1% of arare earth element; up to about 2.0% copper; up to about 1.25% niobiumup to about 0.04% phosphorus; up to about 0.75% silicon; up to about0.03% sulfur; up to about 2.2% tantalum; up to about 0.7% titanium; andup to about 0.035% vanadium.
 5. The alloy of claim 1 also comprising atleast one of hafnium and tantalum.
 6. The alloy of claim I wherein thealloy is comprised of: from 12% to 19% chromium; from 18% to 23%molybdenum; from 0.12% to 0.2% aluminum; from 0.002% to 0.006% carbon;from 0.30% to 0.34% manganese; from 1.0% to 1.7% iron; from 0.05% to0.8% cobalt; from 0.10% to 0.34% tungsten; and from 0.002% to 0.005%boron.
 7. The alloy of claim 6 also comprising: from 0.005% to 0.009%cerium; from 0.01% to 0.06% copper; from 0.001% to 0.004% magnesium;from 0.002 to 0.005% phosphorus; from 0.001% to 0.004% sulfur; and from0.01% to 0.02% vanadium.
 8. A nickel- chromium-molybdenum alloycomprised of: from 12% to 19% chromium; from 18% to 23% molybdenum; upto 3% iron; at least one alloying element selected from the groupconsisting of aluminum, boron, carbon, cobalt, copper, hafnium, iron,manganese, niobium, silicon, tantalum, tungsten, vanadium and zirconium;and a balance of nickel plus impurities; wherein the alloy has a P valueof from 31.2 to 35.9, P being defined as:P=2.46Al+0.19Co+0.83Cr−0.16Cu+0.39Fe+0.59Mn+1.0Mo+0.81Zr+2.15Si+1.06V+0.39W+0.68Nb +0.52Hf+0.45Ta+1.35Ti and thealloy is age hardened at about 1100° F. to about 1325° F. for at least 4hours then cooled to room temperature.
 9. The alloy of claim 8 whereinthe alloy is age hardened in not more than 50 hours.
 10. The alloy ofclaim 8 wherein the alloying elements consist of: up to about 0.5%aluminum; up to 0.02% carbon; up to about 1.5% manganese; up to about2.5% cobalt; up to about 4.5% tungsten; and up to about 0.015% boron.11. The alloy of claim 8 also comprising: up to about 0.1% of a rareearth element; up to about 2% copper; up to about 1.25% niobium; up toabout 0.04% phosphorus; up to about 0.75% silicon; up to about 0.03%sulfur; up to about 2.2% tantalum; up to about 0.7% titanium; and up toabout 0.35% vanadium.
 12. The alloy of claim 8 wherein the alloy is agehardened at about 1200° F. for 48 hours.
 13. A nickel-chromium-molybdenum alloy comprised of: from 12% to 19% chromium; from18% to 23% molybdenum; up to about 0.5% aluminum; up to 0.02% carbon; upto about 1.5% manganese; up to about 3% iron; up to about 2.5% cobalt;up to about 4.5% tungsten; up to about 0.015% boron; and a balance ofnickel plus impurities; wherein the alloy has a P value of from 31.2 to35.9, P being defined as: P=2.46Al+0.19Co+0.83Cr−0.16Cu+0.39Fe+0.59Mn+1.0Mo+0.81Zr+2.15Si+1.06V+0.39W+0.68Nb +0.52Hf+0.45Ta+1.35Ti and thealloy is age hardened at about 1100° F. to about 1325° F. for at least 4hours then cooled to room temperature.
 14. The alloy of claim 13 whereinthe alloy is age hardened in not more than 50 hours.
 15. The alloy ofclaim 13 also comprising: up to about 0.10% of a rare earth element; upto about 2% copper; up to about 1.25% niobium; up to about 0.04%phosphorus; up to about 0.75% silicon; up to about 0.03% sulfur; up toabout 2.2% tantalum; up to about 0.7% titanium; and up to about 0.35%vanadium.
 16. A method for treating an alloy having a compositioncomprised of from 12% to 19% chromium, from 18% to 23% molybdenum, up toabout 0.5% aluminum, up to about 0.015% boron, up to 0.02% carbon, up toabout 2.5% cobalt, up to about 3% iron up to about 1.5% manganese, up toabout 1.25% niobium, up to about 0.75% silicon, up to about 2.2%tantalum, up to about 0.7% titanium, up to about 4.5% tungsten, and thebalance nickel plus impurities, wherein the alloy has a P value of from31.2 to 35.9, P being defined as:P=2.46Al+0.19Co+0.83Cr−0.16Cu+0.39Fe+0.59Mn+1.0Mo+0.81Zr+2.15Si+1.06V+0.39W+0.68Nb +0.52Hf+0.45Ta+1.35Ti the methodcomprised of: age hardening the alloy at about 1100° F. to about 1325°F. for at least 4 hours; and cooling the alloy to room temperature. 17.The alloy of claim 16 wherein the alloy is age hardened in not more than50 hours.
 18. The method of claim 16 wherein the alloy is age hardenedat about 1200° F. for 48 hours.
 19. A method for treating an alloyhaving a composition comprised of from 12% to 19% chromium; from 18% to23% molybdenum; up to about 0.5% aluminum; up to about 0.015% boron; upto 0.02% carbon; up to about 2.5% cobalt; up to about 3% iron; up toabout 1.25% niobium; up to about 0.75% silicon up to about 2.2%tantalum; up to about 0.7% titanium; up to about 1.5% manganese; up toabout 4.5% tungsten; and a balance of nickel plus impurities; whereinthe alloy has a P value of from 31.2 to 35.9, P being defined as:P=2.46Al+0.19Co+0.83Cr−0.16Cu+0.39Fe+0.59Mn+1.0Mo+0.81Zr+2.15Si+1.06V+0.39W+0.68Nb +0.52Hf+0.45Ta+1.35Ti the methodcomprised of: age hardening the alloy at about 1100° F. to about 1325°F. for at least 4 hours; and cooling the alloy to room temperature. 20.The method of claim 19 wherein the alloy is age hardened in not morethan 50 hours.
 21. The method of claim 19 wherein the alloy is agehardened at about 1200° F. for 48 hours.